The present invention relates to the field of instrumented rolling bearings equipped with an assembly for detecting rotation parameters such as the angular position, the direction of rotation, the speed and the acceleration.
Such instrumented bearings and such set-ups are well known, particularly from document FR-A-2,754,903. These instrumented bearings may be used, for example, for controlling electric: motors of the synchronous type.
The detection assembly consisting of a sensor unit and an encoder element therefore provides the motor control system with all the information it needs, particularly the rotational speed and the position of the poles of the rotor with respect to those of the stator.
In this type of instrumented bearing, the sensor is placed in a unit solid with the non-rotating ring of the bearing, while an encoder element is arranged on the rotating ring of the bearing or on a rotating part of the fixture and rotates past the sensitive part of the sensor so as, in collaboration therewith, to generate a signal that is representative of the rotation of the rotating element. The sensor-encoder assembly may, for example, be of the optical type, or may alternatively be of the magnetic type.
In synchronous motors, the rotor shaft is mounted to rotate in a casing which houses the stator, via at least two rolling bearings, one of which is axially immobilized with respect to the casing via its outer ring, while the outer ring of the other bearing can move axially over a limited distance with respect to the said casing.
The fixture generally comprises spring washers which apply, to the outer ring of the axially free bearing, an axial load which allows the two bearings to run without clearance and with a certain angle of contact that is oblique with respect to the axis of rotation of the bearing, by virtue of the axial preload applied.
In fixtures of the prior art, use is made of detection systems which are separate from the bearings, this being relatively bulky or expensive, or alternatively, use is made of an instrumented bearing placed at the end where the bearing is axially stationary with respect to the casing. Now, certain constraints, particularly those of size, geometry of the surrounding parts, risks of contamination, etc., do not always readily allow an instrumented bearing to be fitted at the end where the bearing is axially stationary in the casing.
There are therefore some technical applicationsxe2x80x94electric motors or the likexe2x80x94in which it would be advantageous to be able to fit an instrumented bearing capable of experiencing a limited axial movement within its housing. The structure of instrumented bearings of the prior art does not allow these to be adapted for mounting these with the outer ring of the bearing free to move axially in its housing.
The object of the invention is to overcome the abovementioned drawbacks and to propose an instrumented rolling bearing capable of slight axial movement with respect to its non-rotating support.
The instrumented rolling bearing device according to the invention is of the type comprising an outer ring, an inner ring, at least one row of rolling bodies arranged between two raceways of the outer and inner rings, and an assembly for detecting rotation parameters, this assembly comprising a sensor unit solid with the non-rotating ring and a rotating encoder member. The device comprises means for both angularly immobilizing a non-rotating part of the device on a support and allowing relative axial movement of the device with respect to the support once the non-rotating part has been definitively mounted on the said support.
A rotating part of the device is solid with a shaft.
Advantageously, the sensor unit and the non-rotating ring are solidly attached.
The sensor unit may comprise the angular-immobilization means.
Advantageously, the angular-immobilization means also constitute means for angularly indexing the sensor unit with respect to the support.
Advantageously, the sensor unit comprises at least one cylindrical outer surface on which the angular-immobilization means are provided.
In one embodiment of the invention, the angular-immobilization means comprise a projection protruding radially from the cylindrical outer surface. The angular-immobilization means may comprise a recess formed between two projections protruding radially from the cylindrical outer surface, the said recess running axially.
The angular-immobilization means may also comprise a projection protruding axially from the sensor unit.
In another embodiment of the invention, the angular-immobilization means comprise a groove set into the cylindrical outer surface, the said groove running axially.
The encoder member may be of the optical or magnetic type.
Another subject of the present invention is the use of a device as described hereinabove. The non-rotating part of the device is mounted on a support provided with means that complement the angular-immobilization means so that the non-rotating part is angularly solid with the support and free to move axially with respect to the said support once the non-rotating part has been definitively mounted on the said support. The said complementing means may comprise an axial peg, a radial finger, or alternatively, a hole formed in the support.
Thus, the assembly formed by the bearing equipped with its sensor unit has a degree of axial freedom in two opposite directions with respect to the stationary support in or on which it is mounted. The unit also angularly immobilizes the non-rotating ring of the bearing with respect to the stationary support.
The device according to the invention therefore comprises means which are able simultaneously, not only while the non-rotating part is being mounted on its stationary support but also after it has been definitively mounted, to:
angularly immobilize a non-rotating part of the device with respect to the stationary support;
possibly angularly index the sensor unit with respect to the stationary support;
provide the possibility of axial movement of the said device with respect to the said stationary support.
Thus, in the case of an instrumented rolling bearing mounted in a synchronous motor, precise angular indexing of the sensor with respect to an element of the casing whose angular position with respect to the stator is known, makes it possible, if the encoder is itself indexed with respect to the shaft and to the poles of the rotor, to ascertain the angular position of the rotor with respect to the stator and therefore the relative position of the poles. The sensor-encoder assembly may also deliver information relating to the speed and acceleration of the rotor. The possibility of axial movement of the instrumented rolling bearing is maintained after definitive mounting, which makes it possible to overcome any possible axial dimensional variations of certain components as a result, for example, of thermal expansions or of variations in the axial loading of the bearings.
Advantageously, these indexing means may also be used for locating the sensor unit connecting wires so that they lead out at a predetermined point.